The electronic spectroscopy of isolated tetrahydrofuran (THF) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.8-10.6 eV with absolute cross-section measurements derived. In addition, an electron energy loss spectrum was recorded at 100 eV and 10A degrees over the 5-11.4 eV range. The He(I) photoelectron spectrum was also collected to quantify ionisation energies in the 9-16.1 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground state of the positive ion. The excellent agreement between the theoretical results and the measurements allows us to solve several discrepancies concerning the electronic state spectroscopy of THF. The present work reconsiders the question of the lowest energy conformers of the molecule and its population distribution at room temperature.